The broad objective of this proposal is to examine how spinal circuits are functionally and structurally organized to generate different motor behaviors. Although there is some good information about how spinal circuits generate particular motor behaviors, such as swimming in lampreys or frog embryos, much less is known about how multiple different behaviors are produced using the available circuitry in spinal cord. The major goals for this proposal are to determine the contribution of different classes of spinal interneurons in different motor behaviors, to examine the synaptic connectivity of interneurons active in these different behaviors, and to examine the patterns of activity within a pool of spinal interneurons not only within a single behavior, but also between different behaviors. Larval zebrafish will be the model system used for this study. The translucent nature of this preparation combined with functional imaging techniques and recent advances in genetic methods permits the means to monitor identified neurons in vivo during various behaviors and thus to correlate neuronal activity to behavior. In brief, this study will examine how spinal circuits are organized to generate swimming and struggling behaviors in zebrafish as a model for how spinal circuits use the available circuitry to produce different motor behaviors